Fix unused_parens false positive #143698
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Fix unused_parens false positive #143698
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| #![allow(warnings)] | ||
| trait MyTrait {} | ||
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|
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| fn foo(_: Box<dyn FnMut(&mut u32) -> &mut (dyn MyTrait) + Send + Sync>) {} |
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How does this behave with dyn FnMut(&()) -> &(dyn Trait) (i.e. one bound that is parenthesized)?
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I've added that case to the test: We continue to emit a warning.
lcnr
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Jul 23, 2025
compiler/rustc_lint/src/unused.rs
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| let own_constraint = self.in_no_bounds_pos.get(&ty.id).copied(); | ||
| let constraint = own_constraint.unwrap_or(NoBoundsException::OneBound); | ||
| self.in_no_bounds_pos.insert(mut_ty.ty.id, constraint); |
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in a sense we want tis to be constraint = own_constraint.max(NoBoundsException::OneBound) where as NoBoundsException::OneBound is currently the minimal value this is correct?
I would feel safer if we were to make this a match on own_constraint or add a NoBoundsException.merge function or sth 🤔
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in a sense we want tis to be
constraint=own_constraint.max(NoBoundsException::OneBound)where asNoBoundsException::OneBoundis currently the minimal value this is correct?
Correct.
I would feel safer if we were to make this a match on
own_constraintor add aNoBoundsException.mergefunction or sth 🤔
I see where you're coming from. I went with the match because 1) I don't see this sprawling and 2) the Option makes the alternatives a bit "messy". Happy to take this any other direction though. 🙂
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thx, sorry for the slow review! @bors r=lcnr,compiler-errors rollup |
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…compiler-errors Fix unused_parens false positive Resolves rust-lang#143653. The "no bounds exception" was indiscriminately set to `OneBound` for referents and pointees. However, if the reference or pointer type itself appears in no-bounds position, any constraints it has must be propagated. ```rust // unused parens: not in no-bounds position fn foo(_: Box<(dyn Send)>) {} // unused parens: in no-bounds position, but one-bound exception applies fn bar(_: Box<dyn Fn(&u32) -> &(dyn Send)>) {} // *NOT* unused parens: in no-bounds position, but no exceptions to be made fn baz(_: Box<dyn Fn(&u32) -> &(dyn Send) + Send>) {} ```
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…compiler-errors Fix unused_parens false positive Resolves rust-lang#143653. The "no bounds exception" was indiscriminately set to `OneBound` for referents and pointees. However, if the reference or pointer type itself appears in no-bounds position, any constraints it has must be propagated. ```rust // unused parens: not in no-bounds position fn foo(_: Box<(dyn Send)>) {} // unused parens: in no-bounds position, but one-bound exception applies fn bar(_: Box<dyn Fn(&u32) -> &(dyn Send)>) {} // *NOT* unused parens: in no-bounds position, but no exceptions to be made fn baz(_: Box<dyn Fn(&u32) -> &(dyn Send) + Send>) {} ```
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Rollup of 9 pull requests Successful merges: - #140871 (Don't lint against named labels in `naked_asm!`) - #141663 (rustdoc: add ways of collapsing all impl blocks) - #143272 (Upgrade the `fortanix-sgx-abi` dependency) - #143585 (`loop_match`: suggest extracting to a `const` item) - #143698 (Fix unused_parens false positive) - #143859 (Guarantee 8 bytes of alignment in Thread::into_raw) - #144042 (Verify llvm-needs-components are not empty and match the --target value) - #144160 (tests: debuginfo: Work around or disable broken tests on powerpc) - #144431 (Disable has_reliable_f128_math on musl targets) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup of 9 pull requests Successful merges: - #140871 (Don't lint against named labels in `naked_asm!`) - #141663 (rustdoc: add ways of collapsing all impl blocks) - #143272 (Upgrade the `fortanix-sgx-abi` dependency) - #143585 (`loop_match`: suggest extracting to a `const` item) - #143698 (Fix unused_parens false positive) - #143859 (Guarantee 8 bytes of alignment in Thread::into_raw) - #144160 (tests: debuginfo: Work around or disable broken tests on powerpc) - #144412 (Small cleanup: Use LocalKey<Cell> methods more) - #144431 (Disable has_reliable_f128_math on musl targets) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of #143698 - benschulz:unused-parens-2, r=lcnr,compiler-errors Fix unused_parens false positive Resolves #143653. The "no bounds exception" was indiscriminately set to `OneBound` for referents and pointees. However, if the reference or pointer type itself appears in no-bounds position, any constraints it has must be propagated. ```rust // unused parens: not in no-bounds position fn foo(_: Box<(dyn Send)>) {} // unused parens: in no-bounds position, but one-bound exception applies fn bar(_: Box<dyn Fn(&u32) -> &(dyn Send)>) {} // *NOT* unused parens: in no-bounds position, but no exceptions to be made fn baz(_: Box<dyn Fn(&u32) -> &(dyn Send) + Send>) {} ```
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Resolves #143653.
The "no bounds exception" was indiscriminately set to
OneBoundfor referents and pointees. However, if the reference or pointer type itself appears in no-bounds position, any constraints it has must be propagated.